1. Field of the Invention
The present invention relates to an anode for lithium-ion secondary battery including an anode active material layer allowed to insert and extract lithium ions, a lithium-ion secondary battery using the same, and a power tool, an electric vehicle and an energy storage system using the same.
2. Description of the Related Art
In recent years, small electronic devices typified by portable terminals and the like have been widely used, and further size and weight reduction and longer life of the electronic devices have been strongly demanded. Accordingly, as power sources, batteries, in particular, small and lightweight secondary batteries allowed to obtain a high energy density have been developed. Recently, applications of such secondary batteries to not only small electronic devices but also large electronic devices typified by vehicles have been studied.
In particular, lithium-ion secondary batteries utilizing insertion and extraction of lithium ions for charge-discharge reactions holds great promise, because the secondary batteries are allowed to obtain a higher energy density than lead-acid batteries or nickel-cadmium batteries.
The lithium-ion secondary battery includes a cathode, an anode and an electrolytic solution. The anode includes an anode active material layer on an anode current collector, and the anode active material layer includes an anode active material involved in charge-discharge reactions.
As the anode active material, a carbon material is widely used. However, since a further improvement in battery capacity has been demanded recently, it is considered to use silicon or tin. The theoretical capacities of silicon (4199 mAh/g) and tin (994 mAh/g) are much higher than the theoretical capacity of graphite (372 mAh/g), so a significant improvement in battery capacity is expected. In this case, it is considered to use not only a simple substance of silicon or tin but also an alloy, a compound or the like of silicon or tin.
To improve various kinds of performance of the lithium-ion secondary battery, various specific configurations of the lithium-ion secondary batteries have been studied. More specifically, to improve cycle characteristics, a fluorine resin or a polyimide is included in anode active material particles including silicon as a constituent element, for example, as described in Japanese Unexamined Patent Application Publication No. 2007-095563. In this case, an anode material is evaporated with the fluorine resin or the like. In addition to this, to obtain an ion-conductive material with high heat resistance which is used for a solid electrolyte, polyorganosiloxane is used, for example, as described in Japanese Unexamined Patent Application Publication No. 2005-307085.